Optical discs, such as compact discs (CD) and digital versatile discs (DVD) are form of computer readable media which provide extensive storage for digital information. A computer or other optical disc player or reader has an optical disc drive (ODD) which may be used to read from and/or write to one or more sides of the disc. The optical disc drive may include an optical pickup unit (OPU) which may be configured with a laser and sensors adapted for reading and/or writing data to the disc. Various ODDs and OPUs are available, and are manufactured to specifically read and write to an optical disc.
Some optical discs are capable of having data written to the disc and/or having visible or optically detectible text or graphics marked on a surface of the disc. Some computers or other optical disc players or readers may be configured to write data to a disc and/or mark optically visible text and/or graphics onto a surface of the disc. In some such devices, an OPU assembly may be used to write the data and/or optically mark the surface of the optical disc or other light-imageable medium. In order to accurately write data and/or produce optical marks of high image quality it is often important to properly focus the OPU assembly with respect to the surface of the optical disc.